Self-mobile gantry cranes are used for handling cargo containers, truck trailers and other bulky cargo in dock yards, rails yards, and other areas. Typically these cranes include an elevated horizontal gantry beam supported above the ground on legs, forming an inverted "U" shaped frame. The gantry crane is moveable longitudinally on fixed rails, tracks or guidable wheels. The hoisting operation is accomplished by a winch or similar device which raises and lowers cables attached to a lifting frame, hook or other load engaging means from which the load is suspended. Typically, the load carrying cables are attached to one or more trolleys which run transversely along the horizontal gantry beam. This arrangement permits the load to be moved vertically by the hoisting apparatus, transversely by the trolley and longitudinally by moving the entire gantry structure along the ground on its rails or wheels.
Because the load is suspended on flexible cables, longitudinal or transverse movement of the hoisting apparatus tends to cause sway of the load being carried. While excessive sway is not desirable, a certain amount of sway can be accommodated when handling cargo containers and most other bulky cargo. However, when the gantry cranes are being used to handle truck trailers, especially in the operation of placing truck tailer bodies on flatbed rail cars for "piggyback" shipping, sway of the load is particularly undesirable. This is because the truck trailer bodies must be accurately positioned with respect to a "fifth wheel" on the flatbed rail car to which the truck trailers are attached for rail shipment. Therefore, when handling truck trailer bodies, it is customary to provide means on the gantry crane for stabilizing the load against sway.
In the past, efforts to reduce the sway of loads suspended from such gantry crane apparatus have included reeving arrangement in which the hoisting cables diverge outwardly and upwardly and thus tend to resist sway. See, for example, U.S. Pat. No. 3,825,128 and 3,086,661. Other patents have suggested the use of a separate stabilizing system (U.S. Pat. Nos. 3,746,182, 4,273,242) and the use of tag lines (U.S. Pat. No. 3,352,324). Probably the most successful solution has been to provide a horizontal stabilizing beam which is guided on the gantry legs and raised and lowered along with the load lifting frame to provide a stabilizing support. Such structures are shown in U.S. Pat. Nos. 3,161,309, 3,176,853 and 3,251,496.
The use of a horizontal stabilizing beam which rises and falls with the lifting apparatus handling the cargo is not desirable, however, on so-called "combination" gantry cranes which are adapted to handle both truck trailer bodies and cargo containers. This is because, when handling cargo containers, the gantry frame customarily is moved across several rows of containers at one time. The presence of the horizontal stabilizing beam at the top of the load lifting frame prevents the frame from being lowered below the top of the highest row of containers and thus makes it impossible to handle containers lower thwn the highest container in any row over which the gantry frame is operating. For this reason, so-called combination gantry frames typically have included stabilizing devices which are disposed only above the lifting frame itself and which do not extend transversely between the legs of the gantry frame. See, for example, the stabilizing device of U.S. Pat. No. 4,273,242.